This invention relates to drive systems and, more particularly, to the longitudinal movement of magnetic tape or other web material by engaging the web between a pinch roller and capstan.
In moving such a web, particularly a continuous web of magnetic tape of the type used in connection with magnetic tape recording or reproduction apparatus, it is desirable that the tape be driven at a substantially uniform speed without slippage relative to the pinch roller and the capstan. Another desirable goal is that the pinch roller and capstan do not so distort the moving web as to either cause unequal movement or distortion of the moving web.
With particular reference to the continuous tape cartridge systems currently in use, the pinch roller responds to a driven capstan. Through this means, a continuous reel of tape is moved through the cartridge for either being recorded upon or having information played back therefrom. In view of the fact that the pinch roller is the sole means within a cartridge of moving the continuous tape, much attention has been directed at perfecting this means of movement.
Ideally, the contact area between the tape and capstan and tape and pinch roller should be defined by a line tangent to the cylindrical surfaces and coincident with the contact of the capstan and the pinch roller. This ideal situation is complicated by the fact that sufficient pressure must be had between the capstan and the roller to insure movement of the tape. Insufficient pressure can cause the tape to slip. Distortion in the tape engaging surface of the pinch roller can cause the tape material to be pulled at an irregular speed, or distorted. The result is speed distortion in the recording or playback of the information on the tape. Angulation of the pinch roller with respect to the capstan can be another source of slippage or damage of the tape. Since the speed of the tape is determined by the speed of the capstan and pinch roller, distortion in the surface area of the pinch roller under the force of the capstan obviously effects the speed at which the tape moves. The resultant distortion of the information emanating from the magnetic tape is often termed "wow" and "flutter." In addition, the movement of the tape is often measured by an indexing means in the player or recorder. The indexing means is usually responsive to the rotation of the capstan. Tape slippage will, therefore, result in inaccurate indexing.
Over the years, there have been a number of suggestions to overcome the above problems of moving the tape in a cartridge. Thus Kellogg (U.S. Pat. No. 2,276,494) suggests a web feeding apparatus in which the pinch roller comprises a conbination of elastable materials and a relatively inelastable materials. The yieldability of such materials, however, results in the distorted surface area of the roller, thereby causing slippage. Such a device is clearly not suitable for tape reproducing and recording equipment.
Auld (U.S. Pat. No. 3,482,792) suggests that the pinch roller of a cartridge may comprise a resilient rubber-like tire of uniform thickness mounted about a central hub. Such a device, however, bears much of the disadvantages of the aforementioned Kellogg device in that the surface yields and distorts in response to pressure from the capstan. Further, if the cartridge is inserted unevenly into the player so that the axis of the pinch roller is at an acute angle to the axis of the capstan, the tape will be gripped unevenly and, therefore, further slippage will be encountered. Thus, it will be seen that a rubber tire pinch roller introduces problems in the movement of a web. In addition, the tire tends to creep around the hub, thereby introducing moving discontinuities in the pressure roller. Also, the compliance or elasticity of the rubber material may change with age. The existence of hard spots in the rubber, which is well known, may show up as another source of uneveness or discontinuity. Rubber may also "cold set" and form a "flat" if left under pressure against the capstan for an extended time.
Thus, the surface characteristics of rubber is effected by heat and cold and is not as suitable as plastic materials for pinch rollers. The hardness of plastic surfaces and relative resistivity to distortion caused by heat or cold makes it a more desirable pinch roller material.
In an attempt to overcome the defects of rubber and use plastics, Isom (U.S. compliant No. 3,537,661) and Coy (U.S. Pat. No. 3,659,797) have each suggested an inner hub connected to an outer hub by a continuous radially extending web. In the device suggested by Isom, the web extends radially. In the device suggested by Coy, the web has a V cross-section with the apex of the V extending in the axial direction. The inventor suggests that this configuration provides for a more yieldable interconnection between the cylindrical outer wall and cylindrical hub. Both of these devices, however, suffer from several disadvantages. It is intended in both devices that the outer cylindrical wall be yieldable or distort in much the same manner as the rubber tire roller. These devices are generally made of plastic and the webs are intended to provide some flexibility or yieldability which, in many ways, simulates the rubber tire. Thus, it appears an object of both inventions to provide a compliant rim or outer cylindrical wall. However, it is in this very yielding of the wall which accounts for a certain creepage of the tape or distortion in the recording or reproduction of the information on the tape. Further, misalignment between the pinch roller and the capstan cannot be overcome by a mere radial yielding of the internal web. In effect, these devices are believed to merely simulate in plastic the overall effect of the rubber or resilient tire used in prior devices, and do not overcome the problem of slippage and distortion discussed above. What is more, they cannot accomodate an occasional misalignment of the axes of the capstan and pinch roller.